Oil and gas well drilling systems include numerous types of piping, referred to generally as “tubulars.” Tubulars include drill pipes, casings, and other threadably connectable oil and gas well structures. Long “strings” of joined tubulars are typically used to drill a wellbore and to prevent collapse of the wellbore after drilling. Some tubulars are fabricated with male threads on one end and female threads on the other. Other tubulars feature a male thread on either end and connections are made between tubulars using a threaded collar with two female threads. The operation of connecting a series of tubulars together to create a “string” is known as a “make-up” process.
One method for making up threaded tubulars involves a multi-step process employing skilled operators using hydraulically actuated tools known as “power tongs”. Hydraulic power tongs have several limitations. During some portions of the make-up process, the hydraulic power tong should be able to apply a large amount of torque to a threaded tubular in order to completely make-up the connection. However, in other portions of the make-up process, the hydraulic power tongs should be torque-limited in order to protect the tubulars from damage if they are inadvertently cross-threaded. Furthermore, in some portions of the make-up process, the power tongs should be able to rotate the threaded tubular slowly in order to start the threads of the threaded tubular, and yet be able to quickly rotate the threaded tubular in order to create a connection.
While it may be possible to design practical hydraulic power tongs with some of these features, a design with all of these features may be impractical to implement in the harsh conditions of an oil well drilling rig. In addition, the repetitive processing of the tubulars may lead to fatigue and boredom in the skilled operators, thus resulting in inattention to the make-up process. Accordingly, a need exists for an make-up system that can be automated and has a large dynamic range with respect to both torque and rotational speed.